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Abstract

Due to the multifaceted nature of sediments in combination with varying physical-chemical properties of environmental contaminants and a multitude of different living and feeding behaviours of the benthic community, estimation of the toxicological risk associated to polluted sediments appears to get easily hampered. Hence, for a maximum of veracity in sediment assessment, at least applied methods and technologies should provide reliability of gained results. However, little attention is brought to confounding factors that might influence the outcome of such applied research. Moreover, knowledge still lacks on how the various approaches compare and can be combined into a comprehensive investigation strategy. The present study aims at filling parts of these gaps through investigation and characterisation of (1) sediment extraction procedures and (2) whole sediment contact tests. After identifying the main confounding factors within preparation of exhaustive extracts, considerations are formulated regarding procedures with a reduced risk of altering samples. A novel vigorous but completely passive extraction method is then introduced, which works with dialysis over a semipermeable membrane (named membrane dialysis extraction, MDE). Initially, MDE extracts were compared to samples from the Soxhlet extraction protocol in biotests on cytotoxity, embryo toxicity and dioxin-like activity. Following a first application in a study on two riverine sediments, the new approach was part of a comprehensive comparison of five different vigorous leaching techniques. Extracts from another two riverine sediments were tested for their toxic effectiveness with respect to cytotoxity, embryo toxicity, and dioxin-like activity, and a number of compound classes, including PAHs, PCBs and DDXs, were determined chemically. Furthermore, three biomimetic extraction procedures were investigated in parallel. All techniques were evaluated in terms of extraction power and reproducibility. In a further comparative study, MDE, Soxhlet and two biomimetic methods were compared to direct contact exposure using the fish embryo test on Danio rerio. Summarizing all four studies, the ability of MDE, Soxhlet and ASE® to yield toxic substances from sediment samples was evaluated by ranking data from biotests and chemical analyses. The topic of sediment contact tests is initiated by an extensive literature review on the use of fish as a test organism in sediment investigation, covering also direct contact exposure. In order to allow reliable testing of sediments, six contact assays were thoroughly investigated for toxicity thresholds and test conditions. Subsequently, the contact test battery was applied on reference sediments spiked with a cocktail of either heavy metals or of organic substances. Resulting data were evaluated with respect to sensitivity and applicability of the different sediment contact tests. MDE was found to provide extraction powers comparable to automated ASE®-methods for most applications, while working at a reduced risk of alteration of resulting extracts. The Soxhlet procedure also gave overall good agreement with ASE®-based methods and MDE, but results indicate an elevated risk of loss of target analytes. Among the biomimetic approaches, Tenax proved best in replicating results from contact tests, while HBCD extracts revealed vigorous extraction powers in some cases. In general, biomimetic methods revealed strong variability of data among each other, complicating the investigation of the bioavailable contaminant fractions. With the sediment contact assays, toxicity thresholds were derived for all six investigated test systems. Furthermore, one natural as well as one formulated reference sediment for the whole test battery could be identified. The majority of assays returned clear dose-response relations for both sediments contaminated with either heavy metals of organic substances. However, the contact tests gave different sensitivities for the sediment-contaminant combinations and also showed varying steepness of the response curves. Based on the results and available literature data, sediment organic matter, clay content, substance properties and feeding as well as living habits were accounted for the observed differences in contaminant availability. The study concludes that investigations into sediment toxicity are likely to be influenced by a multitude of different parameters. As a consequence, it proposes a comprehensive strategical framework that involves several approaches in sediment toxicity assessment and points out required future developmental effort. Most pressing is an automated procedure for vigorous extraction at moderate temperatures, conceivable to be realized through a combination of ASE-methods and membrane dialysis. Furthermore, increased understanding of contaminant availability and test species behaviour is essential.